The severity of a stenosis or lesion in a blood vessel may be assessed by obtaining proximal and distal pressure measurements relative to the given stenosis and using those measurements for calculating a value of a Fractional Flow Reserve (FFR). FFR is defined as the ratio of a first or distal pressure Pd measured on the distal side of the stenosis and to a second or proximal pressure Pa measured on the proximal side of the stenosis, usually within the aorta. Conventionally, a sensor is placed on a distal portion of a guidewire or FFR wire to obtain the distal pressure Pd, while an external pressure transducer is fluidly connected via tubing to a guide catheter for obtaining the proximal, or aortic (AO) pressure Pa. Calculation of the FFR value provides a stenosis specific index of the functional severity of the stenosis in order to determine whether the blockage limits blood flow within the vessel to an extent that treatment is needed. An optimal or normal value of FFR in a healthy vessel is 1.00, while values less than about 0.80 are generally deemed significant and in need of an interventional treatment. Common interventional treatment options include balloon angioplasty and/or stent implantation.
If an interventional treatment is required, the interventional device, such as a balloon catheter, is tracked over a guidewire to the site of the stenosis. Conventional FFR wires generally are not desired by clinicians to be used as guidewires for such interventional devices. Accordingly, if an interventional treatment is required, the clinician generally removes the FFR wire, inserts a conventional guidewire, and tracks the interventional device to the treatment site over the conventional guidewire.
To address this concern, efforts have been made to utilize catheters (micro-catheters) to take pressure measurements for calculating FFR. Using a catheter with a pressure sensor mounted within a distal shaft to measure the distal pressure Pd, a clinician may use a preferred guidewire for tracking the FFR catheter to the site of the stenosis. If an interventional treatment is required, the guidewire used with the catheter may remain in situ and the interventional device may be tracked over the existing guidewire to the site of the stenosis.
However, the pressure sensor mounted to the distal shaft of the catheter is generally exposed to provide access to the surrounding blood flow. The pressure sensor is a sensitive device and may be damaged by contact during handling or contact with tissue during advancement of the FFR catheter through the tortuous vasculature of a patient before positioning at the desired treatment site. Contact damage may result in errors in the measured distal pressure Pd.
While placing the pressure sensor within the distal shaft may protect the sensor from contact damage, manufacturing of the distal shaft in this configuration is difficult. For example, threading of the sensor wire though the distal shaft, mounting of the pressure sensor, and connection of the sensor wire to the pressure sensor in a confined space inside the distal shaft during manufacturing provides both build and maintenance challenges.
Additionally, as the distal shaft of the FFR catheter advances through the tortuous vasculature of the patient on its way to the desired treatment site, the distal shaft encounters bending forces as it winds its way to the targeted stenosis. When the distal shaft encounters these bending forces, the distal shaft and the pressure sensor mounted within can bend, damaging the delicate electronic pressure sensor. Bending force damage may result in errors in the measured distal pressure Pd.
Accordingly, there is a need for systems, and methods for manufacturing such systems, to reduce the occurrence of contact and bending force damage to a pressure sensor of a distal shaft of a FFR catheter.